1. Field of the Invention
The present invention relates to a solid acid catalyst and a process for producing light olefins from hydrocarbon feeds using the same. More particularly, the present invention pertains to a solid acid catalyst, which exhibits excellent selectivity to light olefins at a low temperature in comparison with any conventional techniques including steam cracking process, and a process of selectively producing light olefins from hydrocarbon feeds (typically, full range naphthas) using the same.
2. Description of the Related Art
Olefins, particularly, light olefins, such as ethylene or propylene, are extensively used in a petrochemical industry, and, typically, the light olefins are produced by conducting thermal cracking of naphthas in the presence of steam, i.e., steam cracking. Various modifications of the steam cracking technology have been attempted so as to cope with reaction conditions such as high temperature and reduction of retention time, and to optimize energy efficiency. However, it is not easy to improve energy efficiency using only simple engineering technical modifications. Nowadays, the steam cracking process has consumed about 40% of the energy used in the total petrochemical industry. Accordingly, in consideration of economic efficiency and the reduction of environmental pollution, an improved process technology, that optimizes energy, saves raw materials, and minimizes the emission of carbon dioxide, is in demand. Typically, light naphthas are used as feeds, however since the light naphthas are more expensive than full range naphthas described later, there exists a limit in terms of economic efficiency. In the conventional steam cracking technology, it is not easy to control the composition of produced olefins, and a lot of heat energy is necessary because the required reaction temperature is on the order of 800-900° C., thus there is a need for improvement.
Furthermore, light olefin compounds may be produced through a FCC (fluid catalytic cracking) process. The FCC process is a catalytic cracking technology using a catalyst in the form of fine particle which behave like a fluid when they are aerated with steam, and is extensively known in the art. In particular, a DCC (deep catalytic cracking) technology is known as a process in which the FCC process is modified to improve the yield of olefins (mainly, propylene) instead of gasoline. Generally, the FCC process employs oils, such as vacuum residues, atmospheric residues, or gas oils, which are heavier than the full range naphthas desirably intended as feeds in the present invention.
With respect to the production of olefins, an olefin conversion process involving catalytic cracking has been suggested, in addition to the above-mentioned steam cracking and FCC processes. Most of these processes use an HZSM-5 as the solid acid catalyst, and related prior arts are as follows.
Japanese Patent Laid-Open No. Hei. 6-192135 discloses a catalytic cracking process (reaction conditions: a reaction temperature of 620-750° C. and a weight hourly space velocity (WHSV) of 1-200 h−1) for producing ethylene and propylene from light naphthas containing C2-12 paraffins (having a density of 0.683 g/cc; and a composition containing 42.7 wt % n-paraffins, 36.1 wt % i-paraffins, 0.1 wt % olefins, 14.0 wt % naphthenes, and 7.1 wt % aromatics; and the paraffins being composed of 0.1 wt % C3, 5.2 wt % C4, 18.7 wt % C5, 19.0 wt % C6, 15.2 Wt % C7, 13.5 wt % C8, 6.1 wt % C9, 0.1 wt % C10, and 0.1 wt % C11) in the presence of HZSM-5 or HZSM-11 catalyst having a SiO2/Al2O3 molar ratio of 150-300. In particular, according to the above process, the conversion efficiency is about 93.6 wt % and the total amount of ethylene and propylene generated is 44.9 wt % under reaction conditions of 680° C. and a WHSV of 25 h−1. However, HZSM-5 or HZSM-11 is used in a catalytic cracking reaction without being pelletized, and steam or inert gas is not introduced during the reaction, thus there is a possibility that the catalyst may be readily deactivated even though the initial activity is excellent. In this regard, an additional technology is required to shape the catalyst.
Meanwhile, Japanese Patent Laid-Open No. Hei. 6-199707 reports a catalytic cracking process for producing ethylene and propylene as main products from light naphthas having C2-12 paraffins. In accordance with this prior art, a hydrogen-type zeolite (SiO2/Al2O3=20-500) catalyst on which 100 ppm wt % iron (Fe) is supported is described to show good selectivity to light olefins. However, the zeolite is used in the catalytic cracking reaction without being pelletized, and steam or inert gas is not employed during the reaction, thus there is a possibility that the catalyst may be readily deactivated even though the initial activity is excellent.
U.S. Pat. No. 6,656,345 discloses catalytic cracking (reaction conditions: 400-700° C., WHSV: 1-1000 h−1, and P: 0.1-30 atm) of hydrocarbons feed containing olefins (having a boiling point of 10-220° C. and containing 10-70 wt % olefins and 5-35 wt % paraffins) to produce propylene with a selectivity of 50% or higher and a ratio of propylene/butylene of 2-4. As such, the used catalyst is zeolite (e.g., zeolite having a structure, such as MFI, MEL, MTW, TON, MTT, FER, or MFS, and being exemplified by ZSM-21, ZSM-38, or ZSM-48) which has pores of about 7 Å and a ratio of silica/alumina of 200 or more.
U.S. Pat. No. 6,566,293 discloses a catalyst useful to produce light olefins. According to this patent, HZSM-5 zeolite, in which at least 10 wt % P2O5 is contained, and Y zeolite as main components (10-40 wt %) are mixed with silica (0-25 wt %) and amorphous alumina (about 10 wt %), pelletized through spray drying, and are sintered at 300-1000° C. to produce the catalyst. Furthermore, U.S. Pat. No. 6,521,563 discloses a method of producing a SAPO molecular sieve which contains 4-20 mol % Si, 40-55 mol % Al, and 30-50 mol % P and has an AEL structure, and its application to a catalyst for naphtha catalytic cracking.
WO 02/10313 A2 pertains to single component and mixed catalyst compositions which are used to selectively produce light olefins through steam cracking of hydrocarbons, such as n-hexane or n-octane, and discloses an extrudated catalyst which comprises oxides of Al, Si and Cr, optionally oxides of alkaline metal (Na, K, Li or the like), and a binder (bentonite) and a method of producing the same. In this connection, the composition of catalyst as aforementioned contains 50-95 wt % SiO2, 3-30 wt % Al2O3, 2-10 wt % Cr2O3, 0-18 wt % alkaline metal oxides, and 10-30 wt % binder.
Meanwhile, U.S. Pat. Nos. 4,248,739 and 4,176,090 disclose a layered compound (for example, bentonite expressed by the Formula (Si8)IV(Al4)VIO20(OH)4) that reacts with polymeric cationic hydroxy inorganic metal oxides, such as aluminum chlorohydrol expressed by the Formula [Al26(O)8(OH)52(H2O)20]10+, so as to achieve chemical pillaring, and is then dehydrated to form aluminum oxide pillars between layers of the layered compound, thereby a porous compound structure that is similar to zeolite is created. It is reported that the layered compound pillared through the above-mentioned method is more stable than a typical layered compound in hydrothermal property. However, there are difficulties in that reflux should be conducted for at least 24 hours and the hydrogen ion concentration (pH) should be precisely controlled during the reaction in order to produce the polymeric cationic hydroxy inorganic metal oxides.
U.S. Pat. No. 6,342,153 and Korean Patent Laid-Open No. 2003-0055172 disclose a method of producing a pillared clay catalyst, which is useful to thermal cracking of heavy oils, and the use of the same. This technology involves a production of porous material through pillaring by use of the layered compound. The method of producing the catalyst according to this technology is as follows. (i) Kaolin and HZSM-5 are modified with a rare earth metal ion and an alkaline earth metal ion, respectively and a pelletized catalyst is prepared using a spray dryer. (ii) Separately, polymeric cationic aluminum hydroxide complexes are prepared. (iii) The palletized catalyst produced in step (i) is pillared by use of the complexes of step (ii) at an appropriate pH to produce the catalyst. In this connection, the composition of the catalyst contains 30-75 wt % layered compound, 0-30 wt % HZSM-5 having a pentasil structure or Y-type zeolite, 10-40 wt % inorganic binder (oxides of Al, Si and/or Zr modified with polyethylene glycol), and 1-10 wt % modifying component (polyethylene glycol, and Mg, Al, K, P or Sn). In this technique, Daqing paraffins having a boiling point of 300-500° C. are catalytically and thermally cracked in the presence of a catalyst in accordance with the aforementioned method (reaction temperature: 700° C., catalyst/oil=10, a WHSV=10 h−1, and H2O/feeds=80 wt %), and C2-C4 olefins are produced at a maximum yield of 53 wt %.
U.S. Pat. No. 6,211,104 discloses a preparation method of catalyst applicable to a thermal cracking process for the production of light olefins, in which the pH of slurry consisting of 10-70 wt % layered compound (Kaolin), 5-85 wt % inorganic metal oxides (amorphous silica-alumina, alumina, silica, or pseudo-boehmite), and 1-50 wt % zeolite (0-25 wt % Y zeolite, and 75-100 wt % high silica zeolite with a pentasil structure which contains P and Al, P and Mg, or P and Ca) is controlled to 2-4, agitation is conducted at 20-80° C., pelletization is carried out using spray drying, and sintering is carried out at 450-650° C. At this time, the high silica zeolite comprises 2-8 wt % P and 0.3-3 wt % Al, Mg or Ca based on the weight of zeolite selected from the group consisting of ZSM-5, ZSM-8, and ZSM-11 having a SiO2/Al2O3 molar ratio of 15-60. The Y zeolite refers to high silica Y zeolite in which 14 wt % or less rare earth metal oxides are included.
WO 01/04785 discloses a production of light olefins and aromatics in which a catalyst containing ZSM-5 and/or ZSM-11 zeolite comes into contact with C4+(compounds having 4 or more carbons) naphthas (boiling point: 27-221° C.). The catalyst is produced from raw material which comprises 5-75 wt % ZSM-5 and/or ZSM-11 zeolite having a SiO2/Al2O3 ratio below 70, 20 wt % or less inorganic oxides (silica or clay), and 0.5-10 wt % P. When the C4+ naphthas are catalytically cracked in the presence of the aforesaid catalyst (reaction temperature: 510-704° C., weight ratio of catalyst/feed: 0.01-30, steam/feed: 5-30 wt %, and WHSV: 1-20 h−1), a ratio of ethylene/propylene (weight ratio) is at least 0.39, and a total amount of ethylene and propylene generated is about 25 wt % based on total products.
WO 03/064039 A1 pertains to a mixed catalyst for DCC (deep catalytic cracking) of n-hexane, n-octane, and light naphthas, which is useful for the selective production of light olefins such as ethylene, propylene, and BTX. In this prior art, the mixed catalyst comprises crystalline microporous silicate (for example, pentasil-type silicate) and mesoporous silica-alumina or ZrO2, and Al2O3, MoOx, LaOx, CeOx, a mixture thereof, or an inorganic binder, such as bentonite, is combined therewith. As such, a weight ratio of micropore/mesopore catalyst components is 0.25-4.0. Particularly, a weight ratio of MoOx/Al2O3 is 0.5-1.5, and bentonite constitutes 9-25 wt % of the total mixed catalyst. However, it is believed that, it is not easy to control a micropore/mesopore distribution and the durability of the pelletized catalyst is poor because the mesoporous material is thermally unstable.
WO 01/81280 A1 discloses a method of producing ethylene and propylene. In the method, a zeolite (TON, MTT) catalyst, which has a pore size index of 23-25, no one-dimensional channels cross-linked with each other, and a diameter of 4.4-4.5 Å, comes into contact with one or more C4-C9 olefins (e.g., a mixture of butane and butene) and is heated. According to the method, a fixed bed reaction is conducted under conditions of a temperature of 450-750° C., pressure of 0.5-10 atm, and a WHSV of 0.5-1000 h−1. According to this prior art, in case that the reaction is carried out using butene as a feed at 525° C. and a WHSV of 2.5 h−1 for 202 hours, the total amount of ethylene and propylene is 91.7 wt %, and a ratio of propylene/ethylene is 4.8.
WO 01/04237 A2 discloses a production of light olefins, in which hydrocarbons containing at least 50 wt % C4-C7 aliphatic hydrocarbons are used as feeds and come into contact with ZSM-5 and/or ZSM-11 having a SiO2/Al2O3 ratio over 300 and containing P. In detail, the catalyst used in this prior art comprises 5-75 wt % zeolite, 25-95 wt % matrix such as silica, alumina and clay, and 0.5-10 wt % P. The reaction conditions include a temperature of 510-704° C., a pressure of 0.1-8 bar, a ratio of catalyst/feed of 0.1-10 (weight ratio), and a space velocity of 1-20 h−1. At this time, the total amount of ethylene and propylene generated is 20 wt % of total products, and a ratio of propylene/ethylene is at least 3.
U.S. Pat. No. 5,171,921 discloses a method for selectively producing C2-C5 olefins. According to the aforementioned method, C3-C20 hydrocarbons, which is a mixture of paraffins and olefins, are catalytically cracked (reaction temperature: 550-600° C., and WHSV: 10-1000 h−1) in the presence of a pelletized catalyst which comprises 10-25 wt % ZSM-5 containing 1-3 wt % P and having a Si/Al ratio of 20-60, and a binder such as silica, Kaolin, and bentonite. It is reported that the performance of ZSM-5 is improved through steam-activation at 500-700° C., and that the conversion and the total amount of ethylene and propylene are 60% and 60 wt %, respectively, when 2-butene is catalytically cracked (reaction temperature: 600° C., and WHSV: 366 h−1).
U.S. Pat. No. 5,232,675 and Korean Patent Application No. 1996-7000207 disclose a method of producing a pentasil-type high silica zeolite catalyst in which RE2O3 is 0.01-0.30, Na2O is 0.4-1.0 and a ratio of SiO2/Al2O3 is 20-60. According to this patent, the disclosed catalyst is better than HZSM-5 in hydrothermal stability.
WO 2004/037951 A1 discloses a method of producing a rare earth element-containing zeolite (SiO2/Al2O3=25-800) catalyst (such as La—Mn/HZSM-5, La—Mn/HZSM-5 and P—La—Mn/HZSM-5) having a pentasil structure, in which manganese (an atomic ratio of manganese to aluminum in zeolite is 0.1-20), zirconium (an atomic ratio of zirconium to aluminum in zeolite is 4-20), and/or phosphorus (0.1-5 wt %) are contained. This patent mentions that the catalyst shows excellent catalytic cracking performance in the presence of steam at a relatively low temperature, and that when n-butane is catalytically cracked at 650° C. and a WHSV of 50 h−1, the conversion is 90.2%, the total amount of ethylene and propylene generated is 51.3 wt %, and the ratio of ethylene/propylene is 2.35. According to the patent, ethylene is generated in a relatively larger amount.
In the light of foregoing, the preparation of the catalysts known in the conventional catalytic cracking arts, can roughly be classified into two categories.
As for a first method, HZSM-5 having a MFI stricture or HZSM-5 modified with P as a main component is physically mixed with an inorganic oxide binder to prepare a pelletized catalyst. However, only ZSM-5 participates in the catalytic cracking, and the binder physically mixed therewith does not show the catalytic activity. Moreover, in order to improve catalytic cracking performance, it is required to control a relative amount of the main component of the catalyst or artificially introduce a component serving as micropores or mesopores, depending on the compositional characteristics of naphthas (for example, when the naphthas become heavy). Hence, it is difficult to optimize preparation conditions of the pelletized catalyst in consideration thereof.
In a second method, in order to produce a pelletized catalyst, pillared layered material is added with HZSM-5 and Y-zeolite, and then an inorganic oxide binder and an additive are introduced thereto. The main component of the catalyst is zeolite having a pore size of 5-6 Å and a three dimensional structure, which is represented by HZSM-5.
However, the catalyst has a drawback in that much time is taken due to the complexity of the synthesis procedures, and reproducibility is poor when the catalyst is commercially produced.
As with the prior arts as discussed above, heavy oils (vacuum residues, atmospheric residues, gas oils and the like), or light oils containing a predetermined content of olefins are typically used as feeds. If heavy oils are used as the feed, undesirably, the yield of light olefins is low. On the other hand, if light oils are used as the feed, a desired yield of light olefins is plausible only when the oils contain the specific olefin content or more.